Currently, in order to determine the correct size, the surgeon has to have available a set of implants in different sizes and evaluate the optimum size of the femur before making the cut. In addition, it is difficult for him to know the impact of the choice of implant size on the cut of the bone and the position of the implant.
This invention aims to overcome these inconveniences by proposing a size measurer which allows the surgeon to determine very simply and very quickly, amongst a given, finite number of femoral implant sizes, first which size exactly corresponds to the femur on which the femoral implant should be implanted and subsequently, if, among those available, there is no size which corresponds exactly to that of the femur, which is the closest, and the exact place where the anterior cut along the femoral axis should be made in order to perfectly position the implant on the anterior cortical, sure of good positioning of the implant's trochlea and reducing patellar surges in vivo, whilst indicating the cut thickness more or less at the level of the posterior condyles.